1. Field of the Invention
This invention relates to a stencil printing drum, which is made up of a rotary cylindrical drum, in the printing section of a stencil printing machine.
2. Description of the Related Art
In general, a stencil printing operation is carried out with a stencil printing machine having a stencil printing drum. The stencil printing drum comprises: a rotary cylindrical drum having an ink passage region and an ink non-passage region; and an ink supplying roller provided inside the rotary cylindrical drum to supply a printing ink onto the inner cylindrical surface of the rotary cylindrical drum. With the machine, a stencil printing operation is carried out as follows: First, a stencil paper which has been perforated is wound on the outer cylindrical surface of the rotary cylindrical drum. Under this condition, a printing ink is supplied from the ink supplying roller provided inside the rotary cylindrical drum so as to be transferred through the stencil paper.
The rotary cylindrical drum is generally made up of a plurality of ink passage sheets laid one on another, and a stencil paper is placed over the outermost ink passage sheet. As is described above, the printing ink is supplied from the ink supplying roller provided inside the stencil printing drum. In this operation, the ink which is not used for printing, namely, an excess of ink may leak outside through the interface of the stencil paper and the ink passage sheet, or it may leak outside flowing through the interfaces of the plurality of ink passage sheets.
In order to overcome this difficulty, the following method has been proposed in the art: An ink bank for preventing the leakage of ink is provided in such a manner as to surround the ink passage region of the outer cylindrical surface of the stencil printing drum, or it is provided at the rear end of the ink passage region of the stencil printing drum as viewed in the direction of rotation of the stencil printing drum.
The above-described ink bank which surrounds the ink passage region of the outer cylindrical surface of the stencil printing drum or is provided at the rear end of the latter, is to stop the ink which otherwise may flow over the outer cylindrical surface of the rotary cylindrical drum. However, the quantity of ink which the ink bank is able to dam up is limited to a certain value. Hence, if the quantity of ink which leaks out is larger than the aforementioned value, then the ink will flow over the ink bank.